Quality packet radio service for a general packet radio system

ABSTRACT

The Quality Packet Radio Service enhances the slow General Packet Radio Service medium access procedure to include fast in-session access capability. In order to maximize spectral efficiency, all services in Quality Packet Radio Service are assigned uplink radio channel resources only when they have active data to send. A new set of common control channels is designed to provide these in-session network access capabilities. These channels support similar access and control functions as the General Packet Radio Service common control channels (such as Packet Random Access Channel, Packet Access Grant Channel) except they are used solely in Quality Packet Radio Service to implement in-session access. These common control channels are structured to meet the stringent low delay requirements for in-session access and are termed fast packet common control channels. Since initial radio channel access to the mobile subscriber station has already been established, a smaller amount of overhead information is required for implementing in-session access, thereby allowing these stringent low delay requirements to be met. Specifically, for those services allowed to use in-session access, the assigned uplink channel resources are released during an in-session inactive data period by releasing its assigned Uplink State Flag(s) and Packet Data Traffic Channel(s).

FIELD OF THE INVENTION

This invention relates to advanced cellular communication networks and,in particular, to a system that improves the performance of existingcellular communication networks by enhancing the slow General PacketRadio Service medium access procedure to include fast in-session accesscapability.

PROBLEM

It is a problem in legacy cellular communication networks to providesubscribers with data services, such as the Internet, and access topacket-switched data communications. This is due to the fact that legacycellular communication networks have a circuit-switched architecturedesigned primarily for voice services, where the network topology ispoint-to-point in nature. This paradigm represents the historical viewof cellular communications as a wireless equivalent of traditionalwire-line telephone communication networks, which serve to interconnecta calling party with a called party. An additional problem in cellularcommunication networks is that the need to concurrently serve many voicesubscribers with the limited bandwidth available in cellularcommunication networks has prevented the provision of wide bandwidthcommunication services, such as data, to these subscribers.

The Internet has emerged as the major driving force behind thedevelopment of new communication network technology. There has also beena worldwide explosion in the number of wireless cellular subscribersthat generates an ever-increasing demand for both ubiquitous untetheredcommunications and constant service availability. The convergence ofthese two powerful trends has fostered an exponential growth in thedemand for mobile access to Internet applications. However, Internet andother data services require the use of packet-switched data networks toobtain the required performance. The legacy first generation (1G) andsecond generation (2G) cellular communication networks have acircuit-switched architecture designed primarily for voice services.This has fostered the development of packet-switched network overlays,termed 2.5G networks, which are implemented over existing secondgeneration (2G) cellular communication networks. The 2.5G networks forman interim solution for providing packet-switched data services toexisting second generation (2G) cellular communication networks untilthe full scale development and deployment of third generation (3G)cellular communication networks that provide both circuit-switched voiceas well as packet-switched data services. Moreover, the 2.5G networkswill thereby provide a legacy platform upon which cost-effective thirdgeneration (3G) cellular communication network upgrades can beimplemented and deployed.

However, a problem with the General Packet Radio Service packet-switchednetwork overlay is that it is designed primarily for providing only besteffort service to bursty data traffic in a spectrally efficient manner.It is extremely well designed for providing this type of service andkeeping the necessary level of compatibility and interoperability withGSM. However, 2.5G systems such as General Packet Radio Service areexpected to eventually migrate in a graceful and cost-effective mannerto full 3G network deployment. Therefore it is extremely desirable forenhancements of these systems to incorporate higher levels of 3Gfunctionality. One of the main attributes of 3G is to enable new serviceapplications. These new service applications are supported through thedefinition of supported 3G service classes with varying degrees ofquality of service (QoS) requirements, including some with much morestringent delay requirements than the best effort service class. TheETSI UMTS Phase 2+ General Packet Radio Service recommendations includethe following service classes:

-   -   Conversation Class—Preserves conversation pattern with stringent        low delay and low error rate requirements. Example: voice        service    -   Streaming Class—Preserves time relation between information        elements of the stream. Example: streaming audio, video    -   Interactive Class—Preserves request response data transfer        pattern and data payload content. Example: web browsing    -   Background Class—Preserves data payload content and best effort        service requirement. Example: Background download of email        messages

The conversational class has the most stringent low delay requirementsfollowed by the streaming class and the interactive class. Thebackground class is essentially delay-insensitive. Presently, theGeneral Packet Radio Service system only supports the Background Classand does not have the functionality to migrate to serve the additionalclasses of service.

SOLUTION

The above-described problems are solved and a technical advance achievedby the present Quality Packet Radio Service which provides enhancementsto the Radio Link Control/Medium Access Control (RLC/MAC) layer protocolof General Packet Radio Service packet-switched network overlay,implemented over existing second generation (2G) cellular communicationnetworks, to support additional classes of service.

It is desirable to enhance the current General Packet Radio Service tobe able to support the additional stringent delay requirements of theadditional service classes to thereby arrive at a single IP-basedintegrated network capable of providing all classes of service fromconversational to best effort data. To be spectrally efficient for allof these service classes, it is necessary to be able to efficientlymultiplex several data sessions with different QoS delay requirements onthe same set of channels. The Quality Packet Radio Service accomplishesthis by enhancing the slow General Packet Radio Service medium accessprocedure to include fast in-session access capability. In order tomaximize spectral efficiency, all services in Quality Packet RadioService are assigned uplink radio channel resources only when they haveactive data to send. A new set of common control channels is designed toprovide these in-session network access capabilities. These channelssupport similar access and control functions as the General Packet RadioService common control channels (such as Packet Random Access Channel,Packet Access Grant Channel) except they are used solely in QualityPacket Radio Service to implement in-session access. These commoncontrol channels are structured to meet the stringent low delayrequirements for in-session access and are termed fast packet commoncontrol channels. Since initial radio channel access to the mobilesubscriber station has already been established, a smaller amount ofoverhead information is required for implementing in-session access,thereby allowing these stringent low delay requirements to be met.Specifically, for those services allowed to use in-session access, theassigned uplink channel resources are released during an in-sessioninactive data period by releasing its assigned Uplink State Flag(s) andPacket Data Traffic Channel(s). However the mobile subscriber station isallowed to maintain its uplink Temporary Flow Identifier. Thus, themobile subscriber station can inform the Base Station Subsystem of itsidentity and the specific Temporary Back Flow being referenced byincluding the Temporary Flow Identifier in its in-session channelrequest message. The Base Station Subsystem can very quickly identifythe mobile subscriber station and the session referenced and assignnecessary uplink resources.

Thus, the Quality Packet Radio Service only requires softwaremodifications and preserves completely the existing networkinfrastructure and appliance hardware, since it is implemented in theMedium Access Control layer of the General Packet Radio Service.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A & 1B illustrate in block diagram for the overall architectureof a second generation (2G) cellular communication network that isequipped with the General Packet Radio Service packet-switched networkoverlay;

FIGS. 2-4 illustrate the General Packet Radio Service time slot andframe structure;

FIG. 5 illustrates the General Packet Radio Service protocol stack;

FIG. 6 illustrates the General Packet Radio Service uplink multiplexing;

FIG. 7 illustrates the message flow for General Packet Radio Serviceaccess procedures;

FIG. 8 illustrates the Quality Packet Radio Service fast uplink anddownlink control channels;

FIG. 9 illustrates the Quality Packet Radio Service uplink accessprocedures for different traffic classes

FIG. 10 illustrates the message flow for Quality Packet Radio Servicefast in-session access procedure

FIG. 11 illustrates the Quality Packet Radio Service generic access andassignment cycles

FIG. 12 illustrates the Quality Packet Radio Service replication Aloharandom access

DETAILED DESCRIPTION OF THE DRAWINGS

In this description, the phrase “third generation cellular communicationnetwork” is used to characterize a network that provides a fullcomplement of packet-based services to mobile subscriber stations. Thetechnical description of the invention is based on the existing GeneralPacket Radio Service packet network overlay on second generation circuitswitched cellular communication networks but it is not intended to limitthe application of the Quality Packet Radio Service to this environment,this architecture is simply used to illustrate the concepts of theQuality Packet Radio Service.

Cellular Communication Network Philosophy

Cellular communication networks 100, as shown in block diagram form inFIGS. 1A & 1B, provide the service of connecting wirelesstelecommunication customers, each having a mobile subscriber station, toboth land-based customers who are served by the common Carrier PublicSwitched Telephone Network (PSTN) 108 as well as other wirelesstelecommunication customers. In such a network, all incoming andoutgoing calls are routed through Mobile Switching Centers (MSC) 106,each of which is connected to a plurality of Radio Network Subsystems(RNS) 131-151 which communicate with mobile subscriber stations 101,101′ located in the area covered by the cell sites. The mobilesubscriber stations 101, 101′ are served by the Radio Network Subsystems(RNS) 131-151, each of which is located in one cell area of a largerservice region. Each cell site in the service region is connected by agroup of communication links to the Mobile Switching Center 106. Eachcell site contains a group of radio transmitters and receivers, termed a“Base Station” herein, with each transmitter-receiver pair beingconnected to one communication link. Each transmitter-receiver pairoperates on a pair of radio frequencies to create a communicationchannel: one frequency to transmit radio signals to the mobilesubscriber station and the other frequency to receive radio signals fromthe mobile subscriber station. The Mobile Switching Center 106, inconjunction with the Home Location Register (HLR) 161 and the VisitorLocation Register (VLR) 162, manages subscriber registration, subscriberauthentication, and the provision of wireless services such as voicemail, call forwarding, roaming validation and so on. The MobileSwitching Center 106 is connected to a Gateway Mobile Services SwitchingCenter (GMSC) 106A as well as to the Radio Network Controllers, with theGMSC 106A serving to interconnect the MSC 106 with the PSTN/IP Network108. In addition, the Radio Network Controllers are connected viaServing GPRS Support Node 106C through the Gateway GPRS Support NodeGGSN 106B to the Internet. The Radio Network Controllers 132, 142, 152at each cell site Radio Network Subsystem 131-151 control thetransmitter-receiver pairs at the Radio Network Subsystem 131-151. Thecontrol processes at each Radio Network Subsystem also control thetuning of the mobile subscriber stations to the selected radiofrequencies. In the case of WCDMA, the system also selects the PN codeword to enhance isolation of the communications with the mobilesubscriber stations.

In FIG. 1B, the mobile subscriber station 101 is simultaneouslycommunicating with two Base Stations 133 & 143, thus constituting a softhandoff. However, a soft handoff is not limited to a maximum of two BaseStations. When in a soft handoff, the Base Stations serving a given callmust act in concert so that commands issued over RF channels 111 and 112are consistent with each other. In order to accomplish this consistency,one of the serving Base Stations may operate as the primary Base Stationwith respect to the other serving Base Stations. Of course, a mobilesubscriber station 101 may communicate with only a single Base Stationif this is determined to be sufficient by the cellular communicationnetwork.

The control channels that are available in this system are used to setup the communication connections between the subscriber stations 101 andthe Base Station 133. When a call is initiated, the control channel isused to communicate between the mobile subscriber station 101 involvedin the call and the local serving Base Station 133. The control messageslocate and identify the mobile subscriber station 101, determine thedialed number, and identify an available voice/data communicationchannel consisting of a pair of radio frequencies (and orthogonal codingfor CDMA systems) which is selected by the Base Station 133 for thecommunication connection. The radio unit in the mobile subscriberstation 101 re-tunes the transmitter-receiver equipment containedtherein to use these designated radio frequencies and orthogonal coding.Once the communication connection is established, the control messagesare typically transmitted to adjust transmitter power and/or to changethe transmission channel when required to handoff this mobile subscriberstation 101 to an adjacent cell, when the subscriber moves from thepresent cell to one of the adjoining cells. The transmitter power of themobile subscriber station 101 is regulated since the magnitude of thesignal received at the Base Station 133 is a function of the subscriberstation transmitter power and the distance from the Base Station 133.Therefore, by scaling the transmitter power to correspond to thedistance from the Base Station 133, the received signal magnitude can bemaintained within a predetermined range of values to ensure accuratesignal reception without interfering with other transmissions in thecell.

The voice communications between mobile subscriber station 101 and othersubscriber stations, such as land line based subscriber station 109, iseffected by routing the communications received from the mobilesubscriber station 101 through the Telephone Switching Center 106 andtrunks to the Public Switched Telephone Network (PSTN) 108 where thecommunications are routed to a Local Exchange Carrier 125 that servesland line based subscriber station 109. There are numerous MobileSwitching Centers 106 that are connected to the Public SwitchedTelephone Network (PSTN) 108 to thereby enable subscribers at both landline based subscriber stations and mobile subscriber stations tocommunicate between selected stations thereof. Data communicationsbetween mobile subscriber station 101 and other data communicationsystems, such as server 120, is effected by routing the datacommunications received from the mobile subscriber station 101 throughIP network 107. This architecture represents the present architecture ofthe wireless and wire-line communication networks.

General Packet Radio Service

General Packet Radio Service (GPRS), as shown in FIG. 1A, is a packetnetwork overlay that can be deployed to provide a 2.5G packet switchedupgrade of the TDMA-based second generation (2G) circuit switchedcellular communication networks: Global System for Mobile Communications(GSM), and the North American IS-136. The implementation of the QualityPacket Radio Service in the General Packet Radio Service packet networkoverlay on GSM cellular communication networks is described herein, inview of its present dominant position in serving over 70 percent ofworldwide cellular subscribers. The extension of the General PacketRadio Service to the North American IS-136 cellular communicationnetwork is analogous to the implementation disclosed herein and thedescription of this implementation is omitted in the interest ofbrevity.

The General Packet Radio Service overlay over the circuit-switched GSMcellular communication network provides an independent IP-basedpacket-switched core network. The present evolution of General PacketRadio Service is designed primarily for providing best-effort packetservices and permits IP-based applications such as Internet access in anefficient manner. However, a problem with the General Packet RadioService packet-switched network overlay is that it is designed primarilyfor providing only best effort service to bursty data traffic in aspectrally efficient manner.

The focus of the present Quality Packet Radio Service is to developenhancements to the Radio Link Control/Medium Access Control (RLC/MAC)layer protocol of General Packet Radio Service to enable the provisionof all the other traffic classes—Class 1 through Class 4 as specified byETSI (European Telecommunications Standards Institute) UMTS (UniversalMobile Telephone System) Phase 2+ General Packet Radio Servicerecommendations—that will be supported by future 3G systems. Theseclasses are:

Conversational Voice, video telephony (very low latency) StreamingMultimedia (preserve internal time relationship) Interactive Webbrowsing, games (preserve data integrity) Background E-mail (timeinsensitive, preserve data integrity)These are termed Quality of Service (QoS) and the frame error rates canvary from a 10% frame error rate to 10⁻⁶ bit error rate. For CDMAsystems, the lower the bit error rate, the higher the spreading sequencemeaning more transmit power and bandwidth are used with a correspondinghigher Quality of Service. From the mobile subscriber station'sperspective, the Quality of Service and occupied base-band data rateaffect the final encoded data rate on a frame-by-frame basis, the callappears, in its functionality, to be circuit switched and continuous innature. This is particularly true when in soft or softer handoff.

These Quality Packet Radio Service enhancements are made in the MAC/RLClayer of the General Packet Radio Service protocol stack only. Henceonly software upgrades of the Mobile Station (101) and the Base StationSubsystem (BSS) are necessary and no hardware modifications arerequired. The GSM physical layer, TDMA time slot and framing structuresare preserved, thereby allowing legacy GSM handsets to continue tofunction in a Quality Packet Radio Service overlay of GSM. Finally, theQuality Packet Radio Service core network is compatible with theproposed EDGE (Enhanced Data for GSM Evolution) upgrade to 8-PSKmodulation as well as UMTS W-CDMA for a clear migration path to eventual3G systems.

The Quality Packet Radio Service only requires software modificationsand preserves completely existing network infrastructure and appliancehardware since it is primarily related to the medium access controllayer. Therefore, the following description is focused on thecorresponding General Packet Radio Service RLC/MAC protocol layer.

General Packet Radio Service Network Architecture

In order to understand the operation of the Quality Packet RadioService, the underlying architecture of the General Packet Radio Serviceis described. The following description relates to the portion of theGeneral Packet Radio Service that implements the Radio LinkControl/Medium Access Control (RLC/MAC) protocol layer.

The General Packet Radio Service network architecture, since it wasoriginally designed to overlay GSM networks, is heavily based on GSMsystem concepts to achieve the maximum amount of interoperability and torequire the least amount of additional infrastructure and modificationsfor implementing the overlay. The General Packet Radio Service enabledmobile subscriber stations (MS) communicate directly across the same GSMphysical radio links with the GSM base station transceivers located inthe cell sites. In the GSM Public Land Mobile Network (PLMN), basestation controllers (BSC) control the radio links between the mobilesubscriber station and the Base Station Transceiver, and a Base StationTransceiver and its associated BSC is called a Base Station Subsystem(BSS). The base station controllers are connected to the GSM Public LandMobile Network backbone through mobile switching centers (MSC), whichprovide the switching, routing and transfer of intra-GSM Public LandMobile Network voice, message and control signals. The gateway mobileswitching center (GMSC) is the interface of the GSM Public Land MobileNetwork to the public switched telephone network (PSTN). Communicationsbetween network elements in a GSM Public Land Mobile Network employSignaling No. 7 (SSN7).

The General Packet Radio Service overlay adds two new network routerelements: the Serving General Packet Radio Service Support Node (SGSN)and the Gateway General Packet Radio Service Support Node (GGSN).Hardware upgrades of the Base Station Subsystem are also required. AChannel Codec Unit (CCU) is incorporated into an existing Base StationTransceiver to enable General Packet Radio Service specific codingschemes. The Base Station Subsystems are connected to their serving GPRSSupport Node. A Packet Control Unit Support Node (PCUSN) unit is addedto each Base Station Subsystem to support the frame relay packet datainterface between the Base Station Subsystem and the GPRS Support Node.The GPRS Support Nodes serve as the access routers to the General PacketRadio Service core network. The GGSN is the gateway router thatinterfaces the General Packet Radio Service core network to external IPor X.25/X.75 packet data networks (PDN). Circuit switched trafficdestined to the PSTN continue to be routed from the Base StationSubsystem to the MSC and then through the GMSC on to the PSTN. On theother hand, packet switched traffic is independently routed from theBase Station Subsystem through its serving GPRS Support Node over thecore General Packet Radio Service network to the GGSN, and on to PublicPacket Data Networks.

The GSM physical layer is utilized in General Packet Radio Service where200 KHz bandwidth channels are provided at different carrier frequenciesin each cell site. Each 200 KHz channel is further channelized via timedivision multiplexing into 8 time slots per TDMA (time-division multipleaccess) frame. Each slot time is 0.577 msec in duration and each TDMAframe is 4.615 msec in duration. The General Packet Radio Service TDMAtime slot and frame structure is displayed in FIGS. 2-4. Transmissionsbetween different mobile subscriber stations and a Base StationTransceiver can occur within the 8 time slots. A mobile subscriberstation transmits only in certain time slots and its transmitter ispowered off when it is idle to conserve battery power. The mobilesubscriber station's periodic switching of its transmitter on or off iscalled bursting and the transmission during a single time slot is calleda burst. The normal burst of 156.25 bits duration that carries eitheruser traffic or network control signaling is constructed as follows:

Bit Content  1-3 Tail bits (T)  4-60 Coded data (DATA)  61 Stealing flagbit (F)  62-87 Training sequence (TRAIN)  88 Stealing flag bit (F) 89-145 Coded data (DATA) 146-148 Tail bits (T) 148-156.25 Guard period(no transmission) (GUARD)

FIG. 3 displays the detailed structure of the normal burst transmission.The tail bits (T3) and the guard period (GUARD) are guard times used tocompensate for timing jitter and synchronization errors. The stealingflag bits (F1) indicate whether the burst contains user traffic ornetwork control signaling data and the training sequence allows thereceiver to equalize radio propagation multi-path effects. There areonly a total of 114 coded data bits in a normal burst transmission of156.25 bit duration. Only these coded data bits carry user traffic ornetwork control signaling data. The amount of coding depends on thelevel of channel error correction coding selected by the application.

General Packet Radio Service Protocol Architecture

Although it supports applications based on IP and X0.25 (and potentiallyother packet data protocols), General Packet Radio Service specificprotocols are employed within the General Packet Radio Service corenetwork. FIG. 5 gives an illustration of the present version of theGeneral Packet Radio Service protocol stack, the devices in which it islocated and the interfaces between devices. In this structure, thefollowing well-known elements are included:

MS Mobile Subscriber Station BSS Base Station Subsystem SGSN ServingGeneral Packet Radio Service Support Node GGSN Gateway General PacketRadio Service Support Node GTP GPRS Tunnel Protocol SNDCP Sub-NetworkDependent Convergence Protocol BSSGP Base Station GPRS Protocol LLCLogical Link Channel RLC Radio Link Control MAC Medium Access Channel GbInterface between a SGSN and a Base Station Subsystem Um Interfacebetween a mobile subscriber station and a GPRS fixed network part forproviding packet network services Gn Interface between a SGSN and a GGSNGi Interface between the GPRS network and other IP or X.25 networks

The General Packet Radio Service Tunnel Protocol (GTP) is used totransfer packets between two General Packet Radio Service support nodes(e.g. SGSN, GGSN). The Tunnel Protocol encapsulates the IP or X.25packet into a GTP Packet Data Unit (PDU). The GTP Packet Data Unit isrouted over the IP-based General Packet Radio Service backbone networkusing either Transmission Control Protocol (TCP) for X.25-basedapplications or User Data Protocol (UDP) for IP-based applications. Thisprocess is called General Packet Radio Service tunneling. Intransferring IP or X.25 packets between the mobile subscriber stationand its serving GPRS Support Node, General Packet Radio Service uses adifferent set of network protocols, namely, the Sub-Network DependentConvergence Protocol (Sub-Network Dependent Convergence Protocol) andthe Logical Link Control (LLC) layers. The Sub-Network DependentConvergence Protocol is used to map network protocol layercharacteristics onto the specific characteristics of the underlyingnetwork. The Logical Link Control provides a secure logical pipe betweenthe GPRS Support Node and each mobile subscriber station and performssuch tasks as ciphering, flow control and error control. The LogicalLink Control is used by the Sub-Network Dependent Convergence Protocolto transfer network layer Packet Data Units between the mobilesubscriber station and it's serving GPRS Support Node. The Logical LinkControl Packet Data Units are transferred over the radio link using theservices provided by the Radio Link Control/Medium Access Control(RLC/MAC) protocol layer. The RLC/MAC protocol layer exists both withinthe mobile subscriber station and the Base Station Subsystem. Thetransfer of Logical Link Control Packet Data Units between multiplemobile subscriber stations and the core General Packet Radio Servicenetwork uses a shared radio medium. The Radio Link Control layer isresponsible for:

-   -   1. Segmentation and re-assembly of Logical Link Control Packet        Data Units.    -   2. Providing the option of including a link level automatic        repeat request (ARQ) procedure for recovery of uncorrectable        data block transmission errors.

The MAC layer operates between the mobile subscriber stations and theBase Station Subsystem and is responsible for:

-   -   1. Signaling procedures concerning radio medium access control    -   2. Performing contention resolution between access attempts,        arbitration between multiple service requests from different        mobile subscriber stations and medium allocations in response to        service requests.

The RLC/MAC layer performance determines to a large extent themultiplexing efficiency and access delay of General Packet Radio Serviceapplications over the radio interface.

General Packet Radio Service Frame and Data Structures

General Packet Radio Service uses the same physical time slot and TDMAframe structure as GSM. The basic Packet Data Unit between the mobilesubscriber station and the Base Station Subsystem is called a Radio LinkControl block (also called RLC/MAC block). A Logical Link Control PacketData Unit is segmented into an appropriate number of Radio Link Controlblocks. Each Radio Link Control block is structured so that it can bechannel coded and transmitted in an interleaved fashion over 4 timeslots in 4 consecutive TDMA frames. Therefore, the logical channelresource assignment unit in the RLC/MAC layer is one Radio Link Controlblock and its transmission unit in the physical layer uses normal burstsover 4 time slots. As we noted above, there are 114 channel coded databits transmitted in each normal burst. One Radio Link Control blocktransmits 4×114=456 coded data bits. The time to transmit 4 TDMAframes=4×4.615 msec=18.46 msec. However, in GSM a multi-frame structureconsisting of 52 TDMA frames is utilized, where every 13^(th) frame isused for purposes other than data transmission (e.g. channelmeasurements). Therefore, only 48 out of the 52 frames are used for datatransmission and the average time to transmit 4 TDMA dataframes=(4×4.615)×(52/48) msec=20 msec. This results in a maximum datathroughput rate over the radio interface of 456 coded bits every 20msec=22.8 Kbps per channel (note here that the time guard, trainingsequence and control bit overheads in a normal burst are not consideredhere). The actual information throughput rate is much less if the RadioLink Control Radio Link Control header, MAC protocol overhead bits,other control bits and the channel coding error protection bits in eachRadio Link Control block are accounted for. Four different channelcoding schemes CS-1 to CS-4 are defined in the General Packet RadioService standard with the following information throughput rates:

Code Code Rate Throughput (Kbps) CS-1 1/2 8 CS-2 2/3 12 CS-3 3/4 14.4CS-4 1  20

Since there is no channel coding in CS-4 (since code rate=1), thisrepresents the maximum possible information throughput rate of 20 Kbpsper channel. Procedures are however included in General Packet RadioService to allow a mobile subscriber station to utilize several channelssimultaneously, thereby increasing its information throughput rate. Upto 8 channels can be allocated to a single mobile subscriber station atone time.

Each set of 4 TDMA frames containing 8 Radio Link Control blocks iscalled a logical frame. FIG. 2 illustrates the structure of a logicalframe in terms of the underlying TDMA frames. Whereas there are 8 timeslots in each TDMA frame, there are 32 time slots in each logical frame.Since the channel resource assignment unit in the RLC/MAC layer is aRadio Link Control block of normal bursts in 4 time slots, a channelsupporting successive logical frames of these 4 time slots is referredto as a Packet Data Channel (PDCH). The Packet Data Channel may eitherbe in the uplink (mobile subscriber station to Base Station Transceivertransmission) or downlink (Base Station Transceiver to mobile subscriberstation transmission) directions. In General Packet Radio Service, thePacket Data Channel assignments are simplex channels, so that an Uplink(Uplink) Packet Data Channel can be used by one mobile subscriberstation while the Downlink (Downlink) Packet Data Channel occupying thesame time slots may be used by a different mobile subscriber station.The Packet Data Channels are mapped to various different logicalchannels that provide specific data transfer functions. To name a fewthat are useful for the following discussion, a Packet Data Channel thatis used to transfer user data traffic only is called a Packet DataTraffic Channel (Packet Data Traffic Channel), which can be either anUplink or Downlink channel. The Packet Access Grant Channel (PAGCH) is aDownlink channel used by the Base Station Transceiver to convey resourceassignment messages to a mobile subscriber station. The PacketAssociated Control Channel (PACCH), which can be either Uplink orDownlink, conveys network control signaling information and also can beused to convey resource assignment messages to a mobile subscriberstation.

User mobility can place the mobile subscriber stations in a cell atdifferent locations and distances from the Base Station Transceiver,resulting in different transmission propagation delays. So in GSM andGeneral Packet Radio Service networks, precise timing synchronizationmust be acquired and maintained at the mobile subscriber station so thatnormal bursts in different time slots do not overlap. However, in someinstances, such as before a radio link is established, timingsynchronization does not exist and reliable normal burst transmissionsmay not be possible. To avoid this problem, the mobile subscriberstation uses a shorter burst, called a random access burst, which allowsthe Base Station Transceiver to measure the propagation delay to themobile subscriber station and subsequently control the mobile subscriberstation timing by transmitting timing advance information to the mobilesubscriber station. The random access burst is short enough so that nooverlap with other bursts can occur for the largest possible propagationdelay differences in a cell of 35 km radius (this is largest allowablecell size in GSM). The random access burst is therefore used by themobile subscriber station to initiate network channel access requestswhen no timing information is available, and is constructed as follows:

Bit Content  1-8 Tail bits (TAIL)  9-49 Synchronization sequence (SYNC)50-85 Coded data (DATA) 86-88 Tail bits (T) 89-156.25 Guard period (notransmission) (GUARD)

FIG. 4 displays the detailed structure of the random burst transmission.The guard period is sufficiently large to accommodate propagation delayscaused by distances up to 75 km, thus allowing a 35 km cell radius. Along synchronization sequence is provided to allow for more accuratetiming measurements. Considerable error protection is included so the 36coded bits carry at most either 8 or 11 bits of information. A logicalUplink channel called the Packet Random Access Channel (PRACH) isassigned one TDMA time slot to be used by a mobile subscriber station toinitiate network channel access and resource assignment requests.Normally, the Packet Random Access Channel is assigned one time slot perTDMA frame. There are four network channel access initiationopportunities in each logical frame. This is illustrated in FIG. 2,where time slot #1 in every TDMA frame is assigned to be a Packet RandomAccess Channel.

RLC/MAC Multiplexing

The RLC/MAC layer was designed to support best efforts transport serviceof bursty traffic in a spectrally efficient manner. Multiple datastreams can be supported on the same Packet Data Traffic Channel and agiven data stream can be supported using multiple Packet Data TrafficChannels. Data transfer in General Packet Radio Service is accomplishedusing an entity called a Temporary Back Flow (TBF). A Temporary BackFlow is a virtual connection that supports unidirectional transfer ofLogical Link Control Packet Data Units on packet data physical channelsbetween a mobile subscriber station and the Base Station Subsystem. Thisvirtual connection is maintained for the duration of a data transfer andconsists of a number of Radio Link Control blocks. A Temporary Back Flowcan be either open-ended or closed-ended. A closed-ended Temporary BackFlow limits the data to be transferred to the amount negotiated betweenthe mobile subscriber station and the Base Station Subsystem duringinitial network channel access. An arbitrary amount of data can betransferred in an open-ended Temporary Back Flow. Each Temporary BackFlow is identified by a Temporary Flow Identifier (TFI). A TemporaryFlow Identifier is 7 bits long for the uplink and is 5 bits long for thedownlink. The Temporary Flow Identifier assigned by the Base StationSubsystem is unique in each direction, so Radio Link Control blocksdestined for different mobile subscriber stations are differentiated bytheir attached Temporary Flow Identifier embedded in the Radio LinkControl block headers. After the completion of data transfer in asession, the Temporary Back Flow is terminated and its Temporary FlowIdentifier is released.

Downlink multiplexing of multiple data streams on the same Packet DataTraffic Channel is accomplished by assigning each data transfer a uniqueTemporary Flow Identifier. Each mobile subscriber station listens to itsset of assigned downlink Packet Data Traffic Channels and only acceptsRadio Link Control blocks with its Temporary Flow Identifier. So a BaseStation Subsystem can communicate with a mobile subscriber station onany of the Packet Data Traffic Channels assigned to it and can multiplexseveral Temporary Back Flows destined for different mobile subscriberstations on the same Packet Data Traffic Channel.

Uplink multiplexing is accomplished by assigning to each data transfer aset of channels and a unique Uplink State Flag (USF) for each of thesechannels. The Uplink State Flag is 3 bits long, allowing up to 7different data transfers to be multiplexed on one channel (the UplinkState Flag=111 is reserved by the network). The Base Station Subsystemuses a centralized in-band polling scheme to poll the desired mobilesubscriber station. This is accomplished by setting the Uplink StateFlag in the MAC header of the Radio Link Control block transmitted overthe corresponding downlink channel to an appropriate value identifyingthe specific data transfer. Thus, a mobile subscriber station listens toall the downlink channels that are paired with the uplink channelsassigned to it. If its Uplink State Flag appears on a downlink channel,then the mobile subscriber station uses the corresponding uplink channelin the next logical frame to send its data. The operation of thisprocedure is illustrated by the following example given in FIG. 6. Inthis example channel 6 of each uplink logical frame is assigned to bothmobile subscriber station 1 and mobile subscriber station 2. So, afterdetecting its Uplink State Flag in channel 6 of downlink frame 1, mobilesubscriber station 1 can use the corresponding uplink channel (channel 6of the uplink logical frame) in frame 2. Meanwhile, the Uplink StateFlag of mobile subscriber station 2 appears in channel 6 of downlinkframe 2. So mobile subscriber station 2 now has permission to transmiton the corresponding uplink channel in frame 3. The Uplink State Flag ofmobile subscriber station 1 appears next in both channel 6 of thedownlink frames 3 and 4, thereby allowing mobile subscriber station 1 totransmit on the corresponding uplink channels in frames 4 and 5respectively. The data carried by downlink channel 6 in each frame canbe destined to any mobile subscriber station and its recipient isidentified by the Temporary Flow Identifier header in the Radio LinkControl data block. This process realizes the multiplexing of differentusers on the same uplink physical channel. So even though the downlinkRadio Link Control data block may be destined to one mobile subscriberstation, the Uplink State Flag carried in the MAC header of that blockcan be targeted to a different mobile subscriber station.

Medium Access Procedures

General Packet Radio Service allows two types of access procedures fordata transfer: one-phase or two-phase. Both of these procedures areshown in FIG. 7.

One-phase Procedure

The mobile subscriber station sends a packet channel request over aPacket Random Access Channel. As discussed earlier, this random accessburst occupies only 1 TDMA time slot. General Packet Radio Service usesa slotted ALOHA based random access procedure for contention resolutionover the Packet Random Access Channel. The 8 or 11 bit information fieldencrypted in the 36 coded data bits in the random access burst carriesonly a limited amount of information, namely; the reason for the access:whether it is a one-phase or two-phase access or a page response; themobile subscriber station class and radio priority; and the number ofblocks to be transmitted (for page responses only). The identity of themobile subscriber station or the connection and the amount of data to betransmitted (except for page responses) is not included in this channelrequest and is not known by the network at this time.

After receiving the packet channel request, the Base Station Subsystemreplies with a packet uplink assignment message over the Packet AccessGrant Channel paired with the Packet Random Access Channel that wasused. This message contains the resource assignment for the mobilesubscriber station including the carrier frequency, Temporary FlowIdentifier, Uplink State Flag and other parameters so the mobilesubscriber station can transmit over the assigned uplink Packet DataTraffic Channel. However, at this time the network is not aware of themobile subscriber station identity and the service requested.

The Base Station Subsystem sends the Uplink State Flag over the downlinkPacket Data Traffic Channel in the next logical frame paired to theassigned uplink Packet Data Traffic Channel.

The mobile subscriber station hears its Uplink State Flag and beginsdata transfer over the assigned uplink Packet Data Traffic Channel inthe next logical frame. The Radio Link Control block transmittedincludes an extended header with the type of service requested and themobile identity via its Temporary Logical Link Identifier (TLLI).

When the network decodes the Temporary Logical Link Identifiersuccessfully, it sends an acknowledgement to the mobile subscriberstation in an uplink ACK/NAK message over the Packet Associated ControlChannel. Contention resolution is completed on the network side; andafter the mobile subscriber station successfully receives thisacknowledgement, contention resolution is completed also on the mobilesubscriber station side.

Data transfer from the mobile subscriber station to the Base StationSubsystem can continue with the mobile subscriber station listening toits Uplink State Flag to begin data transfer over the assigned PacketData Traffic Channel.

Two-phase Procedure

The mobile subscriber station sends a packet channel request in the samemanner as in the one-phase procedure.

After receiving the packet channel request, the Base Station Subsystemreplies with an uplink assignment message over the Packet Access GrantChannel. This assignment is a single block over an uplink PacketAssociated Control Channel. This message contains the resourceassignment for the mobile subscriber station including the carrierfrequency, Temporary Flow Identifier, time slot and other parameters sothe mobile subscriber station can transmit over the assigned PacketAssociated Control Channel.

The mobile subscriber station sends a detailed packet resource requestmessage over the assigned uplink Packet Associated Control Channel. Thisresource request includes the mobile Temporary Logical Link Identifierand the details of the service request.

In response to this request, the Base Station Subsystem then assigns therequired resources to it using an uplink packet assignment message sentover the Packet Associated Control Channel. This message includes thecarrier frequency, Temporary Flow Identifier and Uplink State Flagparameters so the mobile subscriber station can transmit over theassigned uplink Packet Data Traffic Channels.

The Base Station Subsystem sends the Uplink State Flag over the downlinkPacket Data Traffic Channels in the next logical frame paired to theassigned uplink Packet Data Traffic Channels.

The mobile subscriber station hears its Uplink State Flag and beginsdata transfer over the assigned uplink Packet Data Traffic Channels inthe next logical frame.

The choice of which of these two procedures to use is left to theGeneral Packet Radio Service system operator. The essential differenceis that in the one-phase procedure, the uplink data transfer beginsconcurrently with the service negotiation and mobile verification;whereas, in the two-phase procedure, the uplink data transfer onlybegins after the mobile verification and service negotiation iscompleted. Thus the one-phase procedure can be somewhat faster than thetwo-phase procedure if the requested service negotiation is acceptableby the network and the mobile subscriber station application (a minimumof 3 to 4 logical frame times for the one-phase procedure compared with4 to 5 logical frame times for the two-phase procedure in the absence ofcontention). However, since mobile verification is not achieved prior todata transfer in the one-phase procedure, system operators consider itto be insecure, and favor the two-phase procedure in networkdeployments. Moreover, since the two-phase procedure is currently usedin GSM systems, it is desirable for reasons of compatibility.

Quality Packet Radio Service—Enhancements to General Packet RadioService RLC/MAC Protocol Layer

Deficiencies of General Packet Radio Service Medium Access Procedures

In a General Packet Radio Service system, time slots can be sharedbetween GSM circuit-switched voice and General Packet Radio Servicepacket-switched data services to achieve an overall capacity on demandsystem. Therefore General Packet Radio Service must have a high level ofcompatibility and interoperability with GSM. It must operate within thephysical constraints imposed by the GSM cellular network as well asusing the same physical layer transmission channels. Moreover, ease ofmaintenance and operations is very important for GSM operators, whoprefer General Packet Radio Service procedures to closely mirror similarGSM procedures. This level of compatibility and interoperability extendsto the use of GSM time slot, framing, random burst and normal burststructures in General Packet Radio Service. These constraints limit to alarge extent the multiple access efficiency of General Packet RadioService medium access procedures. It also places correspondingconstraints on the type of enhancements that can be implemented toimprove performance or provide larger variety of supported services.

The General Packet Radio Service system was designed primarily forproviding only best effort service to bursty data traffic in aspectrally efficient manner. It is extremely well designed for providingthis type of service and keeping the necessary level of compatibilityand interoperability with GSM. However, 2.5G systems such as GeneralPacket Radio Service are expected to eventually migrate in a gracefuland cost-effective manner to full 3G network deployment. Therefore it isextremely desirable for enhancements of these systems to incorporatehigher levels of 3G functionality. One of the main attributes of 3G isto enable new service applications. These new service applications aresupported through the definition of supported 3G service classes withvarying degrees of quality of service (QOS) requirements, including somewith much more stringent delay requirements than the best effort serviceclass. The ETSI UMTS Phase 2+ General Packet Radio Servicerecommendations include the following service classes:

-   -   Conversation Class—Preserves conversation pattern with stringent        low delay and low error rate requirements. Example: voice        service    -   Streaming Class—Preserves time relation between information        elements of the stream. Example: streaming audio, video    -   Interactive Class—Preserves request response data transfer        pattern and data payload content. Example: web browsing    -   Background Class—Preserves data payload content and best effort        service requirement. Example: Background download of email        messages

The conversational class has the most stringent low delay requirementsfollowed by the streaming class and the interactive class. Thebackground class is essentially delay-insensitive.

The present General Packet Radio Service system is best suited for thebest of effort background service class with very loose delayrequirements. Data transfer sessions are completely terminated(Temporary Back Flow terminated and Temporary Flow Identifier released)during idle periods in a bursty data stream. After an idle period endswith the arrival of additional data, the slow medium access proceduredescribed above must be re-employed to establish data transfer. Althoughsecure and reliable data transfer is achieved, other service classeswith more stringent QOS delay requirements cannot be efficientlyaccommodated in the current General Packet Radio Service system. Forexample, consider the conversational class packet voice service. It iswell known that voice activity detection combined with statisticalmultiplexing can significantly improve spectrum efficiency. Therefore itis desirable for a voice user to release the channel during a silentperiod and regain access only at the beginning of the next talk spurt.The unused residual capacity in these silent periods can be used tomultiplex additional delay-insensitive services (e.g. best effort data)along with the voice users, thereby increasing the overall networkspectral efficiency. The present General Packet Radio Service systemcannot support this procedure since it would require a packet voice userto terminate its Temporary Back Flow and release its Temporary FlowIdentifier during the silent period. Re-establishment of the datatransfer connection (new Temporary Back Flow and Temporary FlowIdentifier) using the current General Packet Radio Service slow mediumaccess procedure will not satisfy voice traffic QOS latencyrequirements.

It is desirable to enhance the current General Packet Radio Servicesystem to be able to support these additional stringent delayrequirement service classes to arrive at a single IP-based integratednetwork capable of providing all services from conversational to besteffort data. If all services are eventually moved to such a platform,lower operational costs can also be achieved. To be spectrally efficientfor all of these service classes, it is necessary to be able toefficiently multiplex several data sessions with different QoS delayrequirements on the same set of channels. A key requirement is toenhance the slow General Packet Radio Service medium access procedure toinclude fast in-session access capability. That is the objective ofQuality Packet Radio Service.

Quality Packet Radio Service Fast In-Session Medium Access Procedures

In order to maximize spectral efficiency, all services in Quality PacketRadio Service are assigned uplink radio channel resources only when theyhave active data to send. For example, in a packet voice session, uplinkchannels are assigned only during talk spurts. In all services, themobile subscriber station must release the uplink channel when itssession is in an inactive state. For services with stringent low delayrequirements, the mobile subscriber station can use the in-sessionnetwork access procedures to request uplink channel resources when thesession becomes active again with data to send. The objective of theQuality Packet Radio Service RLC/MAC protocol design is to support thisin-session network access by providing the following capabilities:

-   -   Fast uplink access during an on-going session    -   Fast resource assignment for both uplinks and downlinks

These capabilities are provided using the following new set of controlchannels to efficiently implement the in-session access procedure.

Fast Packet Common Control Channels

A new set of common control channels, shown in FIG. 8, is designed toprovide these in-session network access capabilities. These channelssupport similar access and control functions as the General Packet RadioService common control channels (such as Packet Random Access Channel,Packet Access Grant Channel) except they are used solely in QualityPacket Radio Service to implement in-session access. These commoncontrol channels are structured to meet the stringent low delayrequirements for in-session access and are termed “fast packet commoncontrol channels” herein. Since initial access between the mobilesubscriber station and the cellular communication network has alreadybeen established, a smaller amount of overhead information is requiredfor implementing in-session access, thereby allowing these stringent lowdelay requirements to be met. Specifically, for those services allowedto use in-session access, the assigned uplink channel resources arereleased during an in-session inactive data period by releasing itsassigned Uplink State Flag(s) and Packet Data Traffic Channel(s).However the mobile subscriber station is allowed to maintain its uplinkTemporary Flow Identifier. Thus, the mobile subscriber station caninform the Base Station Subsystem of its identity and the specificTemporary Back Flow being referenced by including the Temporary FlowIdentifier in its in-session channel request message to very quicklyidentify the mobile subscriber station and the session referenced,enabling the Base Station Subsystem to assign necessary uplinkresources.

-   -   Specifically, the following fast packet common control channels        are implemented in Quality Packet Radio Service:    -   Unlink Fast Packet Access Channel (F-PACH)—used either as a Fast        Packet Random Access Channel (F-PRACH) or as a Fast Packet        Dedicated Access Channel (F-PDACH).    -   Downlink Fast Packet Control Channel (F-PCCH)—used as a Fast        Packet Access Grant Channel (F-PAGCH) or as a Fast Packet        Polling Channel (F-PPCH).

In a Quality Packet Radio Service system, these channels can be locatedon specific TDMA time slots of some selected carrier frequencies. FIG. 8illustrates the structure of these channels implemented in the firsttime slot of every TDMA frame. Each uplink Fast Packet Access Channelhas a corresponding downlink Fast Packet Control Channel paired with it.

Fast Packet Access Channel

The structure of the Fast Packet Access Channel is similar to that ofthe Packet Random Access Channel in General Packet Radio Service.Messages are transmitted in individual bursts and are not interleavedacross bursts over several TDMA frames. The difference between the twois that Fast Packet Access Channel is used only for in-session accessand never for initial network access. The Fast Packet Random AccessChannel (F-PRACH) and Fast Packet Dedicated Access Channel (F-PDACH) canbe time multiplexed on the same physical channel as determined by thetraffic requirements in each cell site. Specific properties of thesechannels are as follows:

-   -   1. The Fast Packet Random Access Channel (F-PRACH) is used with        the Replication Aloha random access protocol described below for        contention resolution. The information in the message sent over        the Fast Packet Random Access Channel includes the Temporary        Flow Identifier and other identifying information of the        requesting service. For a given Temporary Flow Identifier, the        Base Station Subsystem already has the information necessary to        determine its requirements such as the resources needed and the        assignment priority to make a traffic data channel assignment.    -   2. The Fast Packet Dedicated Access Channel (F-PDACH) is used        for fast dedicated access that is contention-free. It is        therefore useful and reserved for future defined services that        do not permit any QoS delay variability, for example:    -   a. Downlink channel condition measurements—allowing the Base        Station Subsystem to assign a larger number of downlink time        slots to higher quality channels, thereby increasing system        throughputs through dynamic bandwidth assignment.    -   b. In future EDGE systems, dynamic data rate assignment can also        be implemented by allowing higher order PSK modulation for        higher quality channel conditions, thereby increasing the        availability of peak data rates.    -   c. Pilot tracking signal for implementing smart antennas for        increasing system throughputs.    -   d. Timing information to retain synchronization during        in-session inactive data periods.        Fast Packet Control Channel

The Fast Packet Control Channel serves two major functions: to sendaccess grant messages to a mobile subscriber station requestingin-session network access and to send polling messages to specificmobile subscriber stations. The Fast Packet Access Grant Channel(F-PAGCH) and Fast Packet Polling Channel (F-PPCH) can be timemultiplexed on the same physical channel as determined by the trafficrequirements in each cell site. Specific properties of these channelsare as follows:

-   -   The Fast Packet Access Grant Channel is used to transmit channel        assignment messages responding to access requests received over        the paired Fast Packet Access Channel. The assignment message        specifies the time slot number, Uplink State Flag(s) and Packet        Data Traffic Channel(s) and other parameters such as the access        probability parameters for the Replication Aloha random access        procedure described below.    -   The Fast Packet Polling Channel is used to poll different        mobiles for access queries and measurement reports as required.        In-session Fast Access RLC/MAC Protocol

The RLC/MAC protocols used for in-session uplink access in QualityPacket Radio Service make use of the Fast Packet Control Channelsdescribed above, as shown in FIG. 10. The following assumptions are madeto obtain one version of the RLC/MAC protocol that provides in-sessionaccess meeting all the QOS delay requirements of the supported serviceclasses:

-   -   1. The four service classes defined in the ETSI UMTS Phase 2+        General Packet Radio Service recommendations will be supported:        conversational, streaming, interactive and background services.    -   2. All services are assigned radio channel resources only when        they have active data to send. The mobile subscriber station        must release the uplink radio resource during its session when        it is in an inactive state.    -   3. Only the Fast Packet Random Access Channel control channel is        used for initiating the fast in-session access. The channel        assignment is sent by the Base Station Subsystem to the mobile        subscriber station using the Fast Packet Access Grant Channel        control channel paired to the Fast Packet Random Access Channel.        The Fast Packet Dedicated Access Channel control channel is used        only for transmission of low bit rate measurement data from the        mobile subscriber station to the Base Station Subsystem.

The overall access procedure is given in FIG. 9:

At the start of a new data session at step 901, the mobile subscriberstation uses the normal General Packet Radio Service initial accessprocedure 91 (either one-phase or two-phase) starting the process bysending a packet channel request message over a Packet Random AccessChannel at step 902. During this initial access procedure and channelresource assignment by the Base Station Subsystem, the mobile subscriberstation establishes a Temporary Back Flow and obtains a Temporary FlowIdentifier at step 903 and Uplink State Flags and Packet Data TrafficChannel(s) at step 904. An open-ended Temporary Back Flow is establishedfor the conversational, streaming and interactive service classes whileonly a closed-ended Temporary Back Flow is allowed for the backgroundservice class. Moreover, for the purposes of differentiating thein-session random access contention resolution priorities for theconversational, streaming and interactive service classes, classspecific access probabilities are assigned for the Replication Aloharandom access procedure in step 905, as described below.

During Radio Link Control block data transfer from the mobile subscriberstation to the Base Station Subsystem at step 906, the Radio LinkControl layer enables link-level retransmission for the background(process 92), interactive and streaming service data (process 93).Link-level retransmissions are disabled for the conversational servicedata in order to minimize transmission delays for this service class.

At the end of each active data burst period during the session (with nodata available for transmission until the next active data burstperiod):

-   -   a. For the background service, the mobile subscriber station        releases its Temporary Flow Identifier, Uplink State Flag(s) and        Packet Data Traffic Channel(s) at step 907.    -   b. For the conversational, streaming and interactive service        classes, the mobile subscriber station maintains its Temporary        Flow Identifier but releases its Uplink State Flag(s) and Packet        Data Traffic Channel(s) at step 911.        At the start of the next active data burst period in the        session:    -   a. For the background service class, the mobile subscriber        station goes through the entire General Packet Radio Service        initial access procedure (starting by sending a channel request        message over a Packet Random Access Channel at step 908) to        obtain a new uplink channel assignment: Temporary Flow        Identifier, Uplink State Flag(s) and Packet Data Traffic        Channel(s) at step 909.    -   b. For the conversational, streaming and interactive service        classes, The mobile subscriber station starts a fast in-session        access procedure by sending a packet channel request message        containing its Temporary Flow Identifier to the Base Station        Subsystem using a Fast Packet Random Access Channel control        channel along with its service class assigned access probability        parameters in the Replication Aloha random access procedure at        step 912. The mobile subscriber station obtains new Uplink State        Flag(s) and Packet Data Traffic Channel(s) assignments from the        Base Station Subsystem at step 913 through an assignment message        received over a Fast Packet Access Grant Channel control channel        paired with the Fast Packet Random Access Channel.

The Base Station Subsystem can request the mobile subscriber station tosend information like measurement reports by sending these requests overthe fast polling channel Fast Packet Polling Channel. Responses can besent back by the mobile subscriber station to the Base Station Subsystemover assigned Packet Data Traffic Channel(s) or assigned Fast PacketDedicated Access Channel(s) at steps 910, 914, respectively.

Replication Aloha Random Access Protocol

A generic access and acknowledgement cycle of the in-session procedureis shown in FIG. 11. Each fast uplink access request over an uplink FastPacket Random Access Channel control channel occupies one TDMA timeslot. The downlink Fast Packet Access Grant Channel assignment channelspaired with each of the Fast Packet Random Access Channel channels in agiven logical frame are multiplexed in the next downlink logical frame.So a complete access and assignment cycle occupies two logical frames or40 msec duration. If contention is successful in the first accesschannel request, the minimum delay incurred to complete the in-sessionaccess procedure is 40 msec. Each cycle with unsuccessful contentionincreases this delay by 40 msec. It follows that for very fast access,higher contention success probabilities are desired, in particular forthe service classes with more stringent low delay requirements. In orderto improve the contention success probability for random access over theFast Packet Random Access Channel control channels, a Replication Alohaprotocol is proposed. This protocol operates in the following manner:

-   -   1. Each time a mobile subscriber station has a packet channel        request message ready to initiate an in-session access, it        randomly chooses k out of n consecutive Fast Packet Random        Access Channel time slots and sends the same request message        burst over each of these k time slots. Here k/n is the service        class specific access probability assigned by the Base Station        Subsystem to the mobile subscriber station in the initial access        session access procedure which was previously described.    -   2. After sending this channel request, the mobile subscriber        station listens to an uplink assignment message from the Base        Station Subsystem on the Fast Packet Access Grant Channel        control channels paired with the k Fast Packet Random Access        Channel channels it used to send the channel request.    -   3. Upon receiving an access request message correctly, the Base        Station Subsystem ignores any duplicate requests from the same        mobile subscriber station. The Base Station Subsystem sends the        uplink assignment message to the mobile subscriber station on        the Fast Packet Access Grant Channel paired to the first Fast        Packet Random Access Channel control channel over which the        access request message was correctly received.    -   4. If none of the k request message transmissions from the        mobile subscriber station are successfully received (that is,        the mobile subscriber station does not receive any assignment        messages in the expected Fast Packet Access Grant Channel time        slots), it repeats Step 1 again. Step 1 is allowed to be        repeated for only a maximum of K times before the access attempt        is aborted.

The access probability parameters (k,n) can be chosen to satisfy accessdelay requirements for the different QoS service classes. An example ofa possible choice of these parameters may be:

1. Conversational class (k, n) = (2, 8) 2. Streaming class (k, n) = (1,8) 3. Interactive class (k, n) = (1, 16)That is, a conversational service class in-session access attemptrandomly chooses 2 access bursts over the next two logical frames whilethe interactive service class in-session access attempt randomly chooses1 access burst over the next 4 logical frames. FIG. 12 illustrates theReplication Aloha access and assignment cycle where mobile subscriberstation 1 uses access probability parameters (2,4) and mobile subscriberstation 2 uses access probability parameters (1,4).Access Delay Performance Analysis

Replication Aloha is designed to have an access delay advantage over thestandard Aloha random access contention resolution protocol. Certainlythe contention success probability in the absence of any radiotransmission errors is increased by sending multiple copies of therequest message. It should also be noted that the hostile mobile radiotransmission environment could cause a significant rate of transmissionerrors, thereby requiring re-transmissions of incorrectly receivedchannel request messages caused by these errors. Replication Aloha hasthe ability to mitigate these effects as well. Our mathematical analysisshows that the average access delay performance for a k=2 ReplicationAloha protocol was 20 to 40 percent lower than the corresponding averagedelay for the standard Aloha protocol. This analysis also suggested thatusing more than k−2 transmitted copies in Replication Aloha did notyield significant additional performance gains. That is because a largernumber of transmission copies increased the amount of contentiontraffic, thereby canceling the advantage obtained by the redundanttransmissions. So it appears that k=2 Replication Aloha random accessshould be employed in Quality Packet Radio Service to accommodate themore stringent low QoS latency services.

Summary

The Quality Packet Radio Service enhances the slow General Packet RadioService medium access procedure to include fast in-session accesscapability. All services in Quality Packet Radio Service are assigneduplink radio channel resources only when they have active data to sendand a new set of common control channels is designed to provide thesein-session network access capabilities. These channels support similaraccess and control functions as the General Packet Radio Service commoncontrol channels (such as Packet Random Access Channel, Packet AccessGrant Channel) except they are used solely in Quality Packet RadioService to implement in-session access.

1. A method for providing low-delay network access to mobile subscriber stations operable in a cellular communication network that provides packet-switched data communications, comprising: assigning, in response to a service request received from a mobile subscriber station, a radio channel having an uplink channel and a downlink channel to serve said mobile subscriber station; and assigning, in response to a service request received from a mobile subscriber station indicative of active data to be exchanged with said mobile subscriber station, radio channel resources on said assigned radio channel to said mobile subscriber station, comprising: transmitting, via a fast packet access channel, multiple copies of access request messages from said mobile subscriber station to said cellular communication network; and transmitting, via a fast packet control channel, access grant messages to a mobile subscriber station requesting in-session network access.
 2. The method of claim 1 wherein said assigned radio channel has an uplink channel and a downlink channel, said step of assigning radio channel resources comprises: releasing, in response to a communication session executing in said mobile subscriber station entering an inactive state, said uplink channel.
 3. The method of claim 2 wherein said step of releasing radio channel resources comprises: releasing assigned uplink channel Uplink State Flag(s) and Packet Data Traffic Channel(s).
 4. The method of claim 3 wherein said step of releasing radio channel resources further comprises: maintaining the mobile subscriber station uplink Temporary Flow Identifier.
 5. The method of claim 2 wherein said step of assigning radio channel resources further comprises: reassigning, in response to said communication session becomes active again with data to send, radio channel resources on said assigned radio channel to said mobile subscriber station.
 6. The method of claim 5 wherein: said step of assigning a radio channel comprises: implementing a virtual connection that supports unidirectional transfer of Logical Link Control Packet Data Units on packet data physical channels between said mobile subscriber station and a Base Station Subsystem in said cellular communication network, maintaining a Temporary Flow Identifier indicative of the active state of said virtual connection; and said step of assigning radio channel resources further comprises: maintaining at least one Uplink State Flag indicative an identity of a specific data transfer executing in said communication session.
 7. The system of claim 6 wherein said mobile subscriber station transmits data indicative of its identity and the specific virtual connection being referenced by including said Temporary Flow Identifier in its in-session channel request message, said step of assigning radio channel resources enables said Base Station Subsystem to assign uplink resources to serve said virtual connection.
 8. The system of claim 1 wherein said step of assigning radio channel resources further comprises: transmitting, via a fast packet control channel, polling messages to a mobile subscriber station.
 9. The system of claim 1 wherein said step of transmitting via a fast packet access channel transmits said messages in individual bursts in a single data frame.
 10. The system of claim 1 wherein said step of transmitting via a fast packet control channel transmits said messages in individual bursts in a single data frame.
 11. The system of claim 1 wherein said step of assigning radio channel resources multiplexes multiple data streams with different QoS latency requirements over multiple data traffic channels.
 12. The system of claim 1 wherein said step of transmitting via a fast packet control channel transmits control channel measurements and timing measurements to said cellular communication network, said method further comprising: performing at least one of the channel management functions of: dynamically assigning traffic time slots according to channel quality conditions to increase General Packet Radio Service network throughput through dynamic bandwidth assignment, dynamically changing the peak transmission rate according to channel quality conditions for mobile data networks that employ a set of different multilevel modulation schemes, transmitting timing information during inactive periods of a traffic session.
 13. The system of claim 1 wherein said step of assigning radio channel resources transmits multiple copies of a message to reduce average delays caused by both traffic contention and mobile radio channel fading degradations.
 14. A system for providing low-delay network access to mobile subscriber stations operable in a cellular communication network that provides packet-switched data communications, comprising: channel assignment means, responsive to a service request received from a mobile subscriber station, for assigning a radio channel having an uplink channel and a downlink channel to serve said mobile subscriber station; and fast packet channel assignment means, responsive to a service request received from a mobile subscriber station indicative of active data to be exchanged with said mobile subscriber station, for assigning radio channel resources on said assigned radio channel to said mobile subscriber station, comprising: access request transmitting means for transmitting, via a last packet access channel, multiple copies of access request messages from said mobile subscriber station cellular communication network; and access grant transmitting means for transmitting, via a fast packet control channel, access grant messages to a mobile subscriber station requesting in-session network access.
 15. The system of claim 14 wherein said assigned radio channel has an uplink channel and a downlink channel, said fast packet channel assignment means comprises: channel release means, responsive to a communication session executing in said mobile subscriber station entering an inactive state, for releasing said uplink channel.
 16. The system of claim 15 wherein said channel release means comprises: means for releasing assigned uplink channel Uplink State Flag(s) and Packet Data Traffic Channel(s).
 17. The method of claim 16 wherein said channel release means further comprises: means for maintaining the mobile subscriber station uplink Temporary Flow Identifier.
 18. The system of claim 15 wherein said fast packet channel assignment means further comprises: channel reassignment means, responsive to said communication session becomes active again with data to send, for assigning radio channel resources on said assigned radio channel to said mobile subscriber station.
 19. The system of claim 18 wherein: said channel assignment means comprises: temporary flow identifier means for implementing a virtual connection that supports unidirectional transfer of Logical Link Control Packet Data Units on packet data physical channels between said mobile subscriber station and a Base Station Subsystem in said cellular communication network, data flow management means for maintaining a Temporary Flow Identifier indicative of the active state of said virtual connection; and said fast packet access channel means further comprises: means for maintaining at least one Uplink State Flag indicative an identity of a specific data transfer executing in said communication session.
 20. The system of claim 19 wherein said mobile subscriber station transmits data to said fast packet channel assignment means indicative of its identity and the specific virtual connection being referenced by including said Temporary Flow Identifier in its In-session channel request message, said fast packet access channel assignment means enables said Base Station Subsystem to assign uplink resources to serve said virtual connection.
 21. The system of claim 14 wherein said fast packet channel assignment means further comprises: fast packet control channel means for transmitting polling messages to a mobile subscriber station.
 22. The system of claim 14 wherein said fast packet access channel means transmits said messages in individual bursts in a single data frame.
 23. The system of claim 14 wherein said fast packet control channel means transmits said messages in individual bursts in a single data frame.
 24. The system of claim 14 wherein said fast packet channel assignment means multiplexes multiple data streams with different QoS latency requirements over multiple data traffic channels.
 25. The system of claim 14 wherein said fast packet control channel means transmits control channel measurements and timing measurements to said cellular communication network to enable said cellular communication network further comprising: means for performing at least one of the channel management functions of: dynamically assigning traffic time slots according to channel quality conditions to increase General Packet Radio Service network throughput through dynamic bandwidth assignment, dynamically changing the peak transmission rate according to channel quality conditions for mobile data networks that employ a set of different multilevel modulation schemes, transmitting timing information.
 26. The system of claim 14 wherein said fast packet channel assignment means transmits multiple copies of a message to reduce average delays caused by both traffic contention and mobile radio channel fading degradations. 